Mobile wireless communications systems continue to grow in popularity and have become an integral part of both personal and business communications. For example, cellular telephones allow users to place and receive voice calls almost anywhere they travel. Moreover, as cellular telephone technology has increased, so too has the functionality of cellular devices and the different types of devices available to users. For example, many cellular devices now incorporate personal digital assistant (PDA) features such as calendars, address books, task lists, etc.
Such multi-function devices may also allow users to wirelessly send and receive electronic mail (email) messages and access the Internet via a cellular network and/or a wireless local area network (WLAN), for example. Many of these devices include low intermediate frequency (low-IF) receivers. A low-IF receiver has two down conversion stages, i.e., a two step down-conversion to DC of the received radio frequency (RF) signals.
A first down conversion stage operates at a carrier frequency minus an intermediate frequency, and a second down conversion stage operates at the intermediate frequency. The first down conversion stage is a quadrature down converter (complex mixer) that down converts the received RF signals to a complex analog in-phase and quadrature (I/Q) form with a small frequency offset, i.e., a low-IF. The complex analog in-phase and quadrature signals are then digitized so that the second down conversion stage converts these signals to DC using a digital complex mixer.
A problem with receivers, and particularly low-IF receivers, is high current consumption. This is because the first down conversion stage in the low-IF receiver has two independent analog/RF circuit paths that carry the I and Q signal representations. Current consumption is especially problematic for battery operated devices where there is a need for prolonging the life of the battery.